1. Field of the Invention
The present invention relates to a self-closing door apparatus and, more particularly, to a torsion bar apparatus used in a self-closing door apparatus for automatically closing a door by the self-aligning torque which is generated when a torsion bar is twisted, and a torque adjusting device for such a torsion bar apparatus.
This kind of self-closing door apparatus is conventionally adapted to a wide field of refrigerating machines and equipments such as refrigerators and show-cases equipped with a freezer, and is very useful for preventing the cold air from leaking out of the door which is left open. As described in U.S. Pat. No. 4,696,078, the torque for closing a door is generated in most cases by the self-aligning torque of a twisted torsion bar (referred to as torque rod in the above-described U.S. Pat. specification).
According to the above-described U.S. Pat. specification, the upper end of a torsion bar (torque rod) is fixed to a door, and the hexagonal head portion at the lower end of the torsion bar (torsion rod) is engaged with a hexagonal opening of a worm wheel so as to be unable to rotate. When the upper portion of the torsion bar (torque rod) is rotated with the door opening operation, the torsion bar (torque rod) is twisted. The self-aligning torque generated by the twisted torsion bar urges the door to rotate in the direction in which the door is closed.
This structure, however, has the following defects. In this type of self-closing door apparatus, a certain initial torque is necessary in order to stably maintain the closed state of a door, but it is preferable for the user, who feels the weight of the door, that the torque during the opening operation is small. However, the self-aligning torque of the torsion bar increases in proportion to the angle of torsion of the torsion bar. If the gradient of the straight line indicating this proportional relationship is steep, a large force is required for opening the door, thereby deteriorating the operability.
The flexibility of a torsion bar is proportional to the length and inversely proportional to the sectional area thereof. Therefore, if two torsion bars are made of the same material and have the same sectional area, the one having a greater length has a gentler gradient in the straight line which indicates the proportional relationship between the self-aligning torque and the angle of torsion. However, if the length of the torsion bar is increased too much, the torsion bar comes into contact with the electric wiring and the like within the door and involves a fear of impairing the electric wiring.
In the torsion bar (torque rod) described in U.S. Pat. No. 4,696,078, the worm wheel is rotated by a worm so as to adjust the torsional torque of the torsion bar (torque rod), that is, to adjust the initial torque of the torque rod in the door-closed state. According to this structure, the user can freely adjust the torque of the torsion bar generated by the door closing operation. It is also possible to continuously adjust the degree of torsion of the torsion bar (torque rod).
In this structure, however, since the worm wheel is rotated by the worm in order to apply the initial torque to the torsion bar (torque rod), the torsion bar (torque rod) is not twisted by stages. It is therefore difficult to quantitatively detect the torque applied. Especially, in the case of adjusting the torque in the direction of reduction, since the point at which the initial torque is zero is not clear, the degree of torsion is sometimes inconveniently reduced to a point exceeding zero by not only restoring the twisted torsion bar (torque rod) to the original position but further twisting, thereby generating a torque for opening the door.
In addition, in the case of restoring the degree of torsion of the torsion bar (torque rod) to zero when the door is replaced, for example, in order to change the direction in which the door is opened, since the point at which the initial torque is zero is not clear, as described above, the hexagonal head portion of the torsion bar (torque rod) must sometimes be released from the worm wheel in the state in which the torsion bar is still twisted. In this case, when the engagement between the hexagonal head and the worm wheel is cancelled, the torsion bar (torque rod) rotates forcibly, thereby involving a risk of breaking parts or injuring the worker.